\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}{ \frac{1}{n} } { \sum_{ j=0 }^{ n-1 } f_j e^{ 2\pi ijk/n } !!! }\end{equation*}
\end{document}
